Many of today's computers, cellular telephones, and other such devices rely on wireless communication to exchange information with other devices, such as to surf the Internet, send and receive email, and communicate audio and video. Still other devices wirelessly communicate with one another to exchange information such as to manage a fleet of vehicles or other assets, to monitor security information or utility usage in a building, or to control industrial systems.
One such wireless example is the Bluetooth technology that enables a cell phone user to associate and use an earpiece in what is sometimes referred to a personal area network or PAN. Another example is a mesh network, in which a number of devices work together to form a mesh, such that data can be sent from a source device to a destination device via other devices in the mesh network.
In certain radio protocols, a 10-bit preamble is created and repeatedly transmitted enough times for a receiving radio to see the preamble when it is scanning for a transmission. The data encoding format might be, for example, Manchester encoding or Biphase space encoding.
In one approach, the preamble includes a hopping pattern and a channel number. Typically, the hopping number is less than 10; it uniquely identifies radios that can see each other. That is, if two radios have different hopping patterns, they cannot see each other. The channel number is the physical channel number of the channel the transmission is sent on.
The receiving radio, when tuned to a particular channel, knows the pattern that it is looking for. If it does not find this pattern, then it moves on to the next channel. To determine if the channel data is valid, one looks at bit timing, valid “Manchester” encoding, and, eventually, the full preamble pattern itself. If any of these tests fail, the radio switches to the next channel.
Once a radio is “locked” into the preamble, then it will continue listening on the channel, until the full packet is received.